Core formed from powder and motor for vehicle using the same

ABSTRACT

A core formed from powder, such as a stator core for use in a motor for a vehicle, wherein the core is formed from metallic powder and includes an outer part disposed at an inside of the motor, an inner part disposed at an inside of the motor, and a winding part which connects the outer part and the inner part and on which a wire is wound, and to a motor for a vehicle using the same. The winding part is formed to have rounded corners and a height lower than the height of the inner part, and a connection part is obliquely formed between the winding part and the inner part so that the winding part and the inner part are naturally connected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is divisional application of U.S. applicationSer. No. 13/524,305, filed Jun. 15, 2012 which claims priority to KoreanPatent Application No. 10-2011-0130841 filed on Dec. 8, 2011, the entirecontents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a core, particularly a core for amotor, formed from powder which has a high degree of freedom of shape(i.e. which can be formed into a wide variety of shapes), and to a motorfor a vehicle using the core. The core can beneficially be used in placeof a conventional electric steel plate.

2. Description of the Related Art

Because an increasing number of vehicles are manufactured to beelectrically operated and be more environmentally friendly, conventionalvehicle systems that have been driven by hydraulic pressure havedeveloped into systems that are electrically driven. This has caused anincrease in the type and number of motors that are used in vehicles. Forexample, high-grade vehicles may have as many as 100 or more motors.

As the demand for motors has increased in this way, motors are alsorequired to be smaller and more lightweight. For instance, the size andweight of motors have been reduced in such a manner that conventional DCmotors are either structurally changed into BLDC (“brushless DC”) motorsor high-performance magnets are utilized. Furthermore, high frequencyand high rotation of vehicle use may contribute to a further need toincrease the output of the motor and to decrease the size further.

FIG. 1 shows a conventional motor for vehicles, and FIG. 2 shows astator core used in the motor of FIG. 1. Conventionally, a core 30 whichconstitutes a large volume of a motor 70 comprises a laminated electricsteel plate 32. The high flux density, high permeability and highstrength of this electric steel plate 32 provide advantages, and, thus,it is widely applied to a core 30 of a motor for vehicles.

However, the electric steel plate 32 is problematic because only a 2Dmagnetic circuit is formed and the degree of freedom of shape is low.Upon designing the motor 70, the confined structure of the electricsteel plate 32 cannot be easily applied. For example, the core 30comprising the electric steel plate is configured such that a rotor 10is positioned in the core 30 and a wire 60 is wound on the outer surfacethereof. As such, wound wire may be disposed on the outer surface of thecore at a height that increases the core size, and as a result the axiallength of the motor may increase.

Further, the type of wire 60 typically used is a copper (Cu) wire, whichis expensive and has a high density. As a result, use of wound Cu wirecan result in an increase in cost and weight.

Further, the conventional electric steel plate 32 has a low degree offreedom of shape, such that an electric steel plate 32 is generallyformed with undesirably sharp corners. These sharp corners can cause thecoating of the wire 60 to undesirably peel off. To prevent this peeling,an insulating part, such as an insulator 50, is additionally attached tothe outer surface of the core 30 to prevent the coating of the wire frompeeling off.

This related art is merely utilized to enhance understanding about thebackground of the present invention, and should not be regarded asconventional techniques known to those having ordinary knowledge in theart.

SUMMARY OF THE INVENTION

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

Accordingly, the present invention has been made keeping in mind theabove problems encountered in the related art, and an object of thepresent invention is to provide a core formed from powder and a motorfor a vehicle using the same. In particular, according to embodiments ofthe present invention, the core is formed from isotropic powder having ahigh degree of freedom of shape. The isotropic powder is used to form acore for a motor so as to provide a small and lightweight motor, and toreduce the use of wire. According to various embodiments, a copper(Cu)-aluminum (Al) wire is used rather than a pure copper (Cu) wire,thus reducing the weight of the wire significantly (e.g. by amounts upto 50% and greater depending on the relative amounts of Cu and Al).

In order to accomplish the above objects, the present invention providesa core formed from powder. According to embodiments of the invention,the core can be a stator core for use in a motor for a vehicle. Invarious embodiments, the core is formed from metallic powder andcomprises an outer part disposed at an inside of the motor, an innerpart disposed at an inside of the motor, and a winding part whichconnects the outer part and the inner part and on which a wire can bewound. The winding part can beneficially be formed to have round cornersand a height lower than a height of the inner part. A connection partcan further be obliquely formed between the winding part and the innerpart so that the winding part and the inner part are connected.

According to an exemplary embodiment, the core may be formed frommetallic powder comprising pure iron particles having a size of about50˜200 μm coated with a layer of phosphate at a thickness of 100 nm orless (not including zero). According to various embodiments, the coremay be formed by a molding process. According to an exemplaryembodiment, the core is formed by subjecting a metallic powder and alubricant (e.g. a polyamide-based lubricant) to press molding carriedout under suitable conditions, such as at a temperature of about 70˜100°C. and an applied pressure of about 7˜11 ton/cm². After press molding,thermal treatment can be carried out at a suitable heightenedtemperature, such as about 500˜600° C., for about 20˜60 min.

The thus formed core may in some embodiments have a density of about 7˜8g/cc, and a partial density difference may be less than about 0.05 g/cc(not including zero).

According to embodiments of the invention, the winding part may beformed to have a circular or oval cross-section. However, othergeometries can also suitably be used, wherein the outer surface issmooth, and preferably is rounded.

The height of the winding part is preferably greater than the height ofthe inner part, and in various embodiments, the height of the windingpart may be at least 0.7 times the height of the inner part.

According to embodiments of the invention, the height of the outer partmay be equal to or greater than the height of the winding part, and maybe lower than the height of the inner part.

In addition, the present invention provides a motor for a vehicle,comprising a stator core, which is formed from metallic powder.According to various embodiments, the core comprises an outer partdisposed at an inside of the motor, an inner part disposed at an insideof the motor, and a winding part which connects the outer part and theinner part and on which a wire is wound. The winding part may be formedto have round corners and a height lower than a height of the innerpart, and a connection part is formed between the winding part and theinner part so that the winding part and the inner part are connected.Preferably, the connection part is obliquely formed between the windingpart and the inner part. According to some embodiments, a wire wound onthe winding part of the core comprises a combination of aluminum andcopper, preferably an aluminum wire with a copper strip formed aroundthe aluminum wire.

According to various embodiments, he wire may include about 15˜30 vol %of copper based on the total wire composition.

The wire may be formed by providing the copper strip around the aluminumwire and attaching opposite ends of the copper strip using a suitablemethod such as welding.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view showing a conventional motor for a vehicle;

FIG. 2 is a view showing a stator core used in the motor of FIG. 1;

FIG. 3 is a view showing a core formed from powder according to anembodiment of the present invention;

FIG. 4 is a cross-sectional view taken along the line A-A of the core ofFIG. 3;

FIG. 5 is a cross-sectional view taken along the line B-B of the core ofFIG. 3;

FIG. 6 is a view showing the wire of a motor for a vehicle according toan embodiment of the present invention;

FIG. 7 is a view showing a motor for a vehicle according to anembodiment of the present invention; and

FIGS. 8 and 9 are graphs showing the performance of the motor accordingto the embodiment of the present invention and a conventional motor.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, a core formed from powder and a motor for a vehicle usingthe same according to preferred embodiments of the present inventionwill be described in detail while referring to the appended drawings.

FIG. 3 is a view showing a core formed from powder according to anembodiment of the present invention, FIG. 4 is a cross-sectional viewtaken along the line A-A of the core of FIG. 3, and FIG. 5 is across-sectional view taken along the line B-B of the core of FIG. 3.

According to the present invention, the core 100 which is a stator coreadapted for a motor M for a vehicle is formed from metallic powder andcomprises an outer part 140 positioned at the inside of a motor M, aninner part 120 positioned at the inside of the motor, and a winding part160 that connects the outer part 140 and the inner part 120 and on whicha wire 300 is wound. As shown in FIG. 4, the winding part 160 is formedto have rounded corners 162. As shown in FIG. 5, the winding part 160 isfurther provided with a height “b” that is lower than the height “a” ofthe inner part 120, and a connection part 164 is obliquely formedbetween the winding part 160 and the inner part 120 so that the windingpart 160 and the inner part 120 are naturally connected.

The winding part 160 may be formed to have a circular or ovalcross-section, and the height b thereof may be at least 0.7 times theheight a of the inner part. As shown in FIG. 5, the outer part 140 maybe formed to have a height “c”, wherein the height c is equal to orgreater than (as in FIG. 5) the height b of the winding part 160 butwhich is lower than the height a of the inner part 120.

The cross-section of the core 100 formed from powder may be designed asshown in FIG. 4 using a high degree of freedom of shape of isotropicpowder. Such a core may be manufactured so that the corners 162 arerounded or the cross-section thereof is circular or oval.

In contrast, a conventional electric steel plate may have sharp cornersbecause of a low degree of freedom of shape, which can undesirablyresulting in the coating of the wire peeling off. To overcome suchproblems, the outer surface of the core can be covered with a materialsuch as an insulator, so that the coating of the wire is prevented frompeeling off.

According to the present invention, the core formed from isotropicpowder has a high degree of freedom of shape and, thus, may be designedand manufactured with rounded edges. Such a rounded structure mayprevent the coating of the wire from peeling off. Further, when the wireis wound for the same number of turns, the use of the wire per turn maybe decreased due to the rounded edges and, thus, a portion where thewire is exposed to the outside of the core (the “wire ending”) may beshortened.

In the illustrated embodiment, the corners of a mold and a die used toconduct the molding are chamfered so that the corners of the core arerounded. According to various embodiments, the core formed from powderhaving the degree of freedom of shape is manufactured so that thecorners 162 of the core on which the wire is wound are chamfered to beround to about 0.5 R or more. Such corners 162 can prevent the coatingof the wire from peeling off and can decrease the use of the wire perturn.

To reduce the length of the wire ending and the use of the wire, thestructure of the core may be designed to have the structure illustratedin FIG. 5. According to some embodiments, the core can be integrallymanufactured to simplify the manufacturing process and decrease themanufacturing cost, and furthermore, high molding density of the coremay be achieved and the difference in density between the different coreparts may be minimized.

In the cross-section shown in FIG. 5, the height b of the winding part160 is formed to be lower than the height a of the inner part 120.According to an exemplary embodiment, the height b of the winding part160 may be at least 0.7 times the height a of the inner part 120. If theheight ratio is less than 0.7, the difference in density between thecore parts becomes large, undesirably deteriorating magnetic properties.

As shown in the drawing, the connection part 164 is obliquely formedbetween the winding part 160 and the inner part 120 so that they arenaturally connected. If, on the other hand, the connection isorthogonal, burrs may easily form on the molding surface, which must beremoved by further core processing. Further, when a magnetic path movesinwards of the motor, it is difficult to efficiently move the magneticpath because it is narrow. By forming the tilted connection part 164,the generation of burrs may be minimized, thus reducing themanufacturing cost. Also in the formation of the magnetic path wherein amagnetic field generated on the wire moves toward the core end (inwardsof the motor) along the core, the pathway may become more efficientbecause of the wide inner part 120, thereby improving the properties ofthe motor.

Among the core parts, the outer part does not affect the magnetic fielddistribution of the core (by formation of the magnetic path) and theperformance of the motor. Thus, if desired, the outer part 140 may bereduced or eliminated to decrease the weight of the core and the axiallength of the motor.

Specifically, the part where the magnetic field distribution appearstoward the inner part 120 is relatively enlarged, thus increasing theelectromagnetic intensity formed by the wire core to thereby increasethe motor torque. Such a core cannot be shaped using a conventionallaminated electric steel plate. However, the formation of such a shapeaccording to the present invention is possible due to the degree offreedom of shape of the soft magnetic powder. Thus, for example, theouter part 140, which does not aid the formation of the magneticcircuit, may be formed to have the height c which is equal to or greaterthan the height of the winding part 160 but is lower than the height ofthe inner part 120.

According to embodiments of the present invention, the core 100 formedfrom powder may be manufactured using metallic powder comprising pureiron particles having a size of 50˜200 μm and a phosphate coating to athickness of 100 nm or less (not including zero) thereon. This core 100may be obtained by subjecting metallic powder and a polyamide-basedlubricant to press molding under suitable conditions, such as atemperature of 70˜100° C. and a pressure of 7˜11 ton/cm², followed bysuitable thermal treatment, such as at 500˜600° C. for 20˜60 min.

The core thus formed has a density of 7˜8 g/cc, and a partial densitydifference that is less than 0.05 g/cc (not including zero), thusexhibiting high performance.

FIG. 6 is a view showing the wire of a motor for a vehicle according toan embodiment of the present invention, and FIG. 7 is a view showing amotor for a vehicle according to an embodiment of the present invention.

The motor for a vehicle using the core according to an embodiment of thepresent invention comprises a stator core 100 which is formed frommetallic powder and includes an outer part 140 positioned at the insideof the motor M, an inner part 120 positioned at the inside of the motor,and a winding part 160 that connects the outer part 140 and the innerpart 120, wherein the winding part 160 is formed to have rounded corners162 and a height b lower than the height a of the inner part 120 and aconnection part 164 is obliquely formed between the winding part 160 andthe inner part 120 so that they are naturally connected; and a wire 300wound on the winding part 160 of the core 100 and comprising an Al wire320 and a Cu strip 340 formed around the Al wire 320. A rotor 500 isalso disposed in the motor.

The wire 300 may include 15˜30 vol % of Cu based on the totalcomposition, and may be formed by providing the Cu strip 340 around theAl wire 320 and attaching opposite ends 342 of the Cu strip 340 usingwelding or other suitable attachment mechanism.

A CCA (Copper Clad Aluminum) wire having 15˜30 vol % of Cu is, thus,manufactured. If the amount of Cu is less than 15%, electricalconductivity may drastically decrease which can undesirably deterioratethe performance of the motor. In contrast, if the amount of Cu exceeds30%, the weight of Cu increases undesirably increasing the price of thecoil. Thus, an amount of Cu more than 30% is regarded as excessive. ACCA structure for increasing electrical conductivity can be formed usingan Al wire having a purity of 99.7% or more and a Cu strip having apurity of 99.9% or more. Also, the CCA wire having high Cu content maybe obtained by minimizing the thermal effect of the Al wire and using awelding process that creates a thin Cu plate having uniform weldingquality.

For example, a planar Cu strip 340 and the Al wire 320 are prepared, theAl wire 320 is placed on the planar Cu strip 340, and the planar Custrip is formed around the Al by rolling. Then, TIG welding or any othersuitable process is performed to connect the ends 342 of the Cu strip.According to an exemplary embodiment, the welding is carried out at800˜1000° C. at a rate of about 5 mm/s. The thus formed CCA is then usedas the motor wire instead of Cu. CCA has an electrical conductivity thatis 70% that of conventional Cu, and the number of turns of the wire andthe diameter can, for example, be changed from Ø1.5*16 turns toØ1.38*18.5 turns. Thus, the weight of the wire may ultimately be reducedby as much as 50% and even more.

FIGS. 8 and 9 are graphs showing the performance of the motor accordingto the embodiment of the present invention, compared to a conventionalmotor, wherein Example 1 uses a general Cu wire, and Example 2 uses thewire according to the present invention. Under a torque of 0.2 Nmtypically required for a motor, the performance of the motor accordingto the embodiment of the present invention is equal or superior to thatof the conventional motor.

As described hereinbefore, the present invention provides a core formedfrom powder and a motor for a vehicle using the same. According to thepresent invention, the core formed from isotropic powder having a highdegree of freedom of shape is applied to a core for a motor, thusreducing the size and weight of the motor and further reducing theamount of a wound wire.

Also, the core for a motor is designed to have a shape providing highdensity and can be formed from high-density soft magnetic powder using ahigh-density molding process. As such, the core is effective atenhancing the performance of the motor.

Furthermore, a process of forming a Cu—Al wire is provided, wherein theCu—Al wire can be used in a motor instead of conventional Cu wires. Sucha Cu—Al wire can have a weight that is reduced by up to 50% and greater.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A motor for a vehicle comprising: a stator core,which is formed from metallic powder and comprises an outer partdisposed at an inside of the motor, an inner part disposed at an insideof the motor, and a winding part connecting the outer part and the innerpart, wherein the winding part has rounded corners and a height lessthan a height of the inner part, and a connection part connecting thewinding part and the inner part, the connecting part extending obliquelybetween the winding part and the inner part; and a wire wound on thewinding part of the core, the wire comprising a combination of aluminumand copper, wherein the core is formed from metallic powder comprisingpure iron particles having a size of about 50˜200 μm, and a phosphatecoating having a thickness of greater than zero and up to 100 nmthereon, wherein the core has a density of about 7˜8 g/cc, and a partialdensity differences is greater than 0 g/cc and less than about 0.05g/cc.
 2. The motor of claim 1, wherein the wire comprises an aluminumwire and a copper strip formed around the aluminum wire.
 3. The motor ofclaim 1, wherein the wire includes 15˜30 vol % of copper based on atotal composition.
 4. The motor of claim 2, wherein the wire is formedby disposing the copper strip around the aluminum wire and weldingopposite ends of the copper strip.